WASHINGTON — The Central Intelligence Agency is building a secret air base in the Middle East to serve as a launching pad for strikes in Yemenusing armed drones, an American official said Tuesday.

The construction of the base is a sign that the Obama administration is planning an extended war in Yemen against an affiliate of Al Qaeda that has repeatedly tried to carry out terrorist plots against the United States.

The clandestine American operations in Yemen are currently being run by the military’s Joint Special Operations Command, with the C.I.A.’s assistance and with the approval of Yemen’s fragile authoritarian government.

But with Yemen’s embattled government on the brink of collapse, Obama administration officials are concerned that a future government might not support American operations. By putting the operations under C.I.A. control, they could be carried out as a “covert action,” which can be undertaken without the support of the host government.

The construction of the base, first reported by The Associated Press, is further evidence that the administration sees armed drones as the weapon of choice to hunt and kill militants in countries where a large American military presence is untenable. Since he took office, President Obama has drastically escalated the C.I.A.’s bombing campaign in Pakistan using armed drones, and the spy agency has carried out more than 25 strikes there this year.

The American official would not disclose the country where the C.I.A. base was being built, but the official said that it would most likely be completed by the end of the year. Discussions about the C.I.A.’s taking over operations in Yemen began last year, the official said, before the political uprising and violence that broke out in the country in recent months.